This invention has to do with chromatography columns and in particular laboratory columns, i.e. small columns such as are used for bench scale or research work.
Generally speaking a column of the relevant kind (referred to herein as being xe2x80x9cof the kind describedxe2x80x9d) has a column tube and end filter arrangements which, in use, retain a bed of particulate chromatography medium in the column tube between them while allowing the passage of fluid for chromatography. At least one of the end filter arrangements is at the front end of a plunger which is axially slidable along inside the tubular column, makes a seal outwardly against the column tube and incorporates an internal flow conduit communicating along the plunger between a filter portion of the filter arrangement and a rear part of the plunger outside the column tube.
Columns of the kind described are currently available at varying levels of cost and complexity.
The column tube is usually glass.
In sophisticated versions the plunger shaft has outer and inner concentric plastic tubes. The inner tube may be a thick solid tube, with a narrow bore providing the flow conduit. Or it may be a wide-bored tube housing an inmost flexible tube which is the flow conduit. At the front end of the shaft a rubber sealing ring is trapped between end formations of the inner and outer stiff tubes, and the filter arrangement has a porous disk (e.g. a sinter or mesh) clamped over a divergent flow distributing end surface of the inner tube, at the outlet of the flow conduit. The outer stiff tube runs slidably through a plastics end unit screwed onto the end of the column tube. The end unit has a mechanism which may be switched between a free sliding engagement with the plunger""s outer plastics tube (for large axial movements) and a screw-threaded engagement (for fine adjustments). An internal screw engagement is also provided between the inner and outer tubes so that after advancing the plunger to the desired positionxe2x80x94i.e. contacting the end of the bed of mediumxe2x80x94the rubber sealing ring can be squeezed out into sealing contact with the column tube wall by axially compressing it between the end formations of the inner and outer tubes. Internal plunger seals are also provided to prevent leakage from between the internal conduit and the filter element into the interior of the plunger construction, or to the outside of the shaft. These columns give good results but can be very expensive, and are complicated to use and maintain.
Laboratory columns of another, simpler kind use short removable plugs at both ends of the column. The plugs are solid polymeric units having an outer O-ring seal to seal against the glass column wall, a narrow central bore for the fluid flow and a flat annular recess at the inner face which receives the porous filter disc. The plug has a very short travel into the column tube, so the media bed must be carefully filled to the correct depth. The necessarily tight-fitting seal makes it hard work to push the plug into the column end. The outside of the glass tube end is threaded to take a clamping nut which holds the plug in once installed. These columns are simpler and cheaper than known plunger columns of the kind described, but less versatile.
A first proposal herein is that the plunger of a column of the kind described comprises a tubular stem of glass or other formable material, preferably transparent, which defines in one piece the internal fluid flow conduit. The permeable filter element is integrally bonded to the front end of this tubular stem across the internal fluid flow conduit.
In particular the filter element is preferably bonded to the plunger stem by being integrally fused therewith, e.g. by heat-fusing. The materials of the filter element and stem can be selected for compatibility in this respect, e.g. both may be of glass or a suitable thermoplastics material. A preferred version has a glass stem fused to a sintered glass filter element.
Preferably the tubular stem defining the internal fluid flow conduit extends as a one-piece integral whole rearwardly to a rear connection union at the rear of the plunger, i.e. a threaded union, spigot or ferrule. Preferably this union has a joint boundary which is exterior of the plunger stem. Like the integral bonding of the filter element at the front end, this one-piece construction provides a simple means for preventing leakage within the plunger which is a significant difficulty with prior art constructions.
A further proposal, preferably combined with the above, is that a one-piece integral construction joins the permeable filter element and an outwardly-directed sealing portion at or adjacent the front end of the plunger which makes a seal directly against the column tube wall, or which mounts a deformable seal element for making such a seal.
In particular the filter element is preferably bonded to the plunger""s outer wall by being integrally fused therewith, e.g by heat-fusing. Again, use of glass or thermoplastics material for the filter element and plunger outer wall is advantageous in this respect; a sintered glass filter element may be fused to an outer glass wall of the plunger.
A further independent proposal herein, again preferably combined with the above, is that the plunger comprises a tubular stem of glass or other formable material which defines, preferably in one piece, the internal fluid flow conduit, and also an outer plunger wall spaced outwardly from the tubular stem, the outer plunger wall and tubular stem being integrally bonded to one another at the front end of the plunger so as to seal off the internal space of the plunger at the front end. Preferably one or both of the stem and plunger outer wall is/are integrally bonded to the filter element, as in the first and/or second aspects set out above. Again the use of fused glass or other thermoplastics is advantageous. Prevention of leakage to within the plunger structure can therefore be prevented reliably without additional internal sealing components. By combination with the other aspects above, the entire internal fluid flow path from a rear connection union to the permeable filter element can be sealed vis xc3xa1 vis the plunger interior without requiring seal components between discrete mechanical parts. The use of glass or other suitable thermoplastics enables such a construction to be made easily e.g using conventional plastics-forming or glass-blowing techniques. Furthermore the use of a transparent material enables the user to observe the flow of material within the plunger.
An outwardly-directed sealing portion at or adjacent the front end of the plunger may have a plunger wall surface which is shaped e.g by machining or moulding, most preferably a machined glass surface, to fit and seal directly against the column tube wall. The use of ground glass surfaces to make fluid-tight seals is as such well-known in the laboratory context. The present proposal can exploit this in a new way, enabling a special advantage in combination with the other aspects as described above and the transparency available with glass material. Machined glass surfaces are not highly transparent but become so when in wetted contact with another glass surface. The plunger exterior may thus have a cylindrical sealing portion making a fitting seal against the column tube wall interior. This sealing portion may be axially elongate, so as to align the plunger axially in the column and avoid the need for column tube end units as were required in the prior art. The same advantage may be achieved by other plunger constructions providing an axially-elongate fitting engagement inside the column tube, e.g axially-extending fins or the like behind the sealing portion which may itself then be shorter.
The plunger may be made with a deformable e.g resilient sealing element such as a sealing ring, preferably an O-ring seal, fitting around the plunger""s outer wall to make a sealing arrangement against the column tube wall.
The internal fluid flow conduit preferably has an elongate portion of relatively narrow cross section (e.g less than 1 or 2 mm diameter) and a divergent (larger cross-section) distribution portion immediately adjacent to the permeable filter element. Where the internal tubular conduit is provided in a discrete tubular stem within an outer plunger wall, the tubular stem is preferably flared at its lower end to provide this divergence. Again this is easy to do with glass or thermoplastics tubular stems.
Particularly in smaller size columns, the plunger may be essentially a solid rod whose outer surface opposes the column wall, with a narrow central bore for the fluid flow conduit. In this case the front end of the rod may be shaped to form a divergent zone around the front opening of the flow bore.
The plunger can resemble that of a syringe. It may have a head at its rear (outward) end adapted for manual pushing. Preferably a rear connection union for the internal fluid flow conduit emerges transversely from the plunger, below such a head.
The column tube wall may be double-ended as in known constructions, and plungers as described above may be deployed at both ends. More preferably however we propose that one end of the column tube wall has a full-diameter opening receiving the mentioned plunger and the other end is a closed end, converging to a union for an external fluid flow conduit, with a fixed permeable filter element across the column tube adjacent the closed end. The fixed permeable element may be permanently installed, e.g a glass sinter disc fused into a glass column tube wall. Or, a mount may be provided for fixed mounting of an exchangeable filter element.
The volume of the column is typically not more than 100 ml.